1. Field of the Invention
The present invention relates to a method of drying materials and an apparatus therefor for drying a wide variety of materials such as cut flowers including natural flowers and flowering plants, vegetables including leafy vegetables, tuberous vegetables, stalky vegetables and fruiting vegetables, leafy plants such as tobacco, seafoods, meats, laundry including medical laundry, industrial laundry and household laundry, and other materials such as wood and ceramic powder.
2. Description of the Prior Art
In prior art methods of drying flowers, cut flowers are placed inside a pressure reduction tank, and with the pressure reduced to a prescribed level, controlled microwave heating and controlled far infrared heating are carried out to dry the cut flowers.
Now, as for the drying of food, the freeze drying method has been mainly used. For example, instant cup ramen usually comes with clear packages containing thinly sliced green onion and the like which have been freeze dried.
Further, the drying of seafood is mostly carried out naturally or by a hot air drying method.
As for the drying of laundry which has undergone washing, it is usually placed into a drying chamber and subjected to hot air while the inside of the chamber is rotated.
Now, when carrying out these various drying methods, the drying time can be controlled by the use of a timer.
However, in the prior art method of drying flowers described above, when carrying out control of the drying process, a method of detecting the state of the object being dried is necessary in order to know when to stop or pause the microwave heating.
In this connection, such prior art methods do not enable sufficient control of the drying process in accordance with the type of object to be dried.
Further, the freeze drying method mainly used to dry vegetables involves the use of an expensive apparatus and is not very effective for drying thick vegetables. Furthermore, when vegetables such as green onions and the like which have a lot of flavor and aroma are dried in this way and then rehydrated in hot air, much of the flavor and aroma are lost.
Furthermore, when drying seafood with the natural method or the hot air method, it is possible for the seafood to decay due to oxidation as a result of the long time required for such drying. Consequently, these methods are not regarded as clean drying methods. Furthermore, these methods degrade the flavor and nutrient content.
Moreover, even though the hot air drying method is generally used in commercial dryers and laundromat dryers to dry laundry, this method takes too much time, generates static electricity, can not achieve adequate sterilization, shrinks cotton knits and causes damage to the cloth material due to the laundry striking the rotating drum.
Furthermore, the drying time for the drying methods described above are generally controlled with a timer set in accordance with a value determined by experiment. However, because the water content of a material can vary from one object to another, it is not possible to achieve an accurate water content level drying with such timed drying methods.
Furthermore, even in the "Method of Drying Flowers and Apparatus Therefor" of Japanese Patent No. 2,548,090 granted to the present inventor, it is possible for insufficient drying to occasionally occur due to an insufficient establishment of control technology in one part of such patent.
In particular, when the output of microwave energy is high, the rate at which water gets forced out of the objects being dried is too fast, and because the amount of heat energy being used is not sufficient to vaporize water drops that fall onto the inside surface of the pressure reduction tank, this creates a build up of water drops on the inside surfaces of the pressure reduction tank. In this case, even though the objects being dried have almost no water content left, no electric discharge occurs because the water drops on the inside of the pressure reduction tank continue to absorb microwave radiation. As a result, the transmission of microwave radiation continues, and this causes the objects being dried to become partially scorched.
Furthermore, in the case where far infrared heaters are arranged inside the pressure reduction tank, such arrangement must be carefully thought out to prevent the objects being dried from touching the far infrared heaters. Moreover, the pressure reduction tank must be made larger than is necessary in order to accommodate the far infrared heaters which require a relatively large amount of space.